This invention is directed to a method of controlling the resolution of an image formed on a substrate which advantageously minimizes fluid spreading on the substrate by use of an autophobic plate-imaging fluid, thereby avoiding the attendant low resolution and reduced image quality associated with such spreading. This invention is also directed to a method of preparing a printing plate in which such a fluid is used to image the plate by ink jetting onto a substrate to form an image area. The invention is also directed to such a printing plate for lithographic printing, and to a method of copying an image onto a medium.
The offset lithographic printing process has long used a planographic printing plate having oleophilic image areas and hydrophilic non-image areas. The plate is commonly dampened before or during inking with an oil-based ink composition. The dampening process utilizes a fountain solution such as those described in U.S. Pat. Nos. 3,877,372, 4,278,467 and 4,854,969. When water is applied to the plate, the water will form a film on the hydrophilic non-image areas of the plate, but will contract into small droplets on the oleophilic plate image areas. When a roller carrying an oil-based ink composition is passed over the dampened plate, it will be unable to ink the non-image areas covered by the aqueous film, but will emulsify the water droplets on the water repellant image areas, which will then take up ink. The resulting ink image is then typically transferred (xe2x80x9coffsetxe2x80x9d) onto a rubber blanket, which is then used to print onto a medium such as paper.
It has been proposed to apply xe2x80x9cdirectxe2x80x9d ink jet printing techniques to lithographic printing. For example, European Patent Publication No. 503,621 discloses a direct lithographic plate making method which includes jetting a photocurable fluid onto the plate substrate, and exposing the plate to ultraviolet radiation to harden the image area. An oil-based ink may then be transferred to the image area for printing onto a printing medium. There is no disclosure of the resolution of ink drops jetted onto the substrate, or the durability of the lithographic printing plate with respect to printing run length.
It has also been proposed to apply the direct ink jet printing techniques without the additional steps of chemical development. This approach advantageously results in lower production costs and a more environmentally acceptable printing process. However, in such techniques it is difficult to control the xe2x80x9cdot spreadingxe2x80x9d of the fluid which forms the oleophilic ink-accepting portion on the printing plate substrate. Such spreading causes low printing image resolution and reduced image quality. For example, European Patent Application No. 591,916 discloses a water-based ink having a polymer containing anhydride groups which are thermally cross-linked with a hydroxy-functional polymer. This formulation is applied by ink-jetting at room temperature onto a room temperature substrate. However, this formulation does not achieve good control of dot spreading.
U.S. Pat. No. 4,833,486 discloses the apparatus and process for imaging a plate with a xe2x80x9chot meltxe2x80x9d type of ink jet printer. The image is produced by jetting at high temperature a xe2x80x9cphase changexe2x80x9d type of ink which solidifies when it contacts the cooler substrate. The ink becomes instantaneously solid rather than remaining a liquid or gel which is thereafter cured to form a solid. However, such an ink does not provide good resistance to press run due to the wax-type nature of the ink formulation.
U.S. Pat. No. 5,738,013 discloses a xe2x80x9cmedia/fluidxe2x80x9d system used in the manufacture of lithographic plates. The media is a conventional hydrophilic substrate, and the fluid is based on a transition metal complex reactive component. The control of dot spreading via the viscosity differences of the fluid as a function of temperature is not addressed.
U.S. Pat. No. 5,688,864 and European Patent No. 745,568 disclose autophobic water repellent surface treatments. However, these disclosures are not directed to imaging a surface with an autophobic fluid via ink jetting to control dot spreading.
The use of fluorosurfactants in ink jet formulations is also known. For example, Jap. Pat. Appln. No. 08-267902 discloses the use of fluorosurfactants in ink jet formulations, primarily for the purpose of alleviating color-to-color bleeding.
U.S. Pat. No. 5,788,754 discloses a thermal ink jet ink comprising nonionic fluorosurfactants to alleviate color-to-color bleeding and to improve image quality. However, it is disclosed that larger dot sizes are desirable (col. 6, line 67), unlike the invention described here.
U.S. Pat. No. 5,852,075 discloses an ink jet ink comprising a mixture of at least one siloxane, surfactant and at least one fluorinated surfactant which exhibit excellent wetting on hydrophilic surfaces.
Research Disclosure No. 39513 (March 1997) discloses a pigmented ink jet ink comprising fluorinated surfactants to control surface tension to control droplet interaction on the receiver in multicolor ink jet printing. The disclosure is not directed to control of droplet spreading.
European Patent Appln. No. 101,266 discloses a printing method and apparatus where the image area is formed using a fluid which may comprise an anionic surfactant, or may comprise a polymer dissolved in toluene (pp. 20-22), and the fluid may be applied by ink jet (p. 50). The disclosure is not directed to reducing fluid droplet dot size or fluid droplet spreading on a substrate.
In view of the foregoing, it would be advantageous to provide a method of controlling spreading of fluids on substrates, particularly for printing plates. It is one object of this invention to provide such a method, in which an autophobic fluid composition is used for which the spreading on a substrate is reduced. It is another object of this invention to provide a method of preparing a printing plate which provides control of fluid composition spreading, and additionally provides good press run length. In the method of this invention, an autophobic fluid composition is applied by an ink jet printing apparatus to directly image a substrate to which the autophobic fluid composition is matched, thereby producing a printable medium, for example a printing plate. It is yet another object of this invention to provide such a printing plate.
Additional objects of this invention are to provide a method of imaging a printing plate, and a method of printing using such a plate.
The method of this invention is useful to provide a printing plate that avoids chemical development steps. More particularly, the method of this invention is useful to control the resolution of an image formed on a substrate, wherein the method comprises: (a) providing a substrate; (b) applying an image to the substrate by ink jetting onto the substrate a fluid composition comprising at least one surfactant, in which the dot size of the fluid composition on the substrate in the presence of the surfactant is less than the dot size of the fluid composition on the substrate in the absence of the surfactant.
In a preferred embodiment, the fluid composition of the method comprises at least one polymeric compound and an ionic surfactant, the fluid composition being applied to an interfacially matched substrate.
This invention is also directed to a method of preparing a printing plate by ink jetting onto the substrate a fluid composition. This invention is further directed to a method of forming an image on a substrate and to a method of copying an image onto a medium.